Finger grease or cigarette tar, or dust from the grease or tar may adhere to electronic devices, such as laptop computers or cellular phones, depending upon the mode of use. Further, the adhesion of the finger grease to the electronic devices tends to accelerate the propagation of various germs on the surface of the devices. If contamination due to the finger grease, cigarette tar or various germs is left as it is, the appearance of the electronic devices and their cleanliness, by extension, may be ruined. In the meantime, as interest in the anti-bacterial effect in the living environment becomes greater for electronic devices, such as laptop computers or cellar phones, the anti-bacterial properties to a chassis and operation keys have come to be demanded. Consequently, in the field of the electronics devices, the introduction of anti-bacterial and anti-fouling technologies as an appropriate response to contamination due to finger grease, cigarette tar or various germs has been desired.
In recent years, a photo-catalystic function in some semiconductor substances, such as titanium oxide (TiO2), has been noticed, and it has been known that the anti-bacterial effect and the anti-fouling effect can be demonstrated based upon the photo-catalystic function. In semiconductor substances that have a photo-catalystic function, in general, the absorption of a light that has energy, which is equivalent to a band gap between a valence band and a conduction band, results in the transition of electrons in the valence band to the conduction band, which electron transition causes the generation of a positive hole in the valence band. Electrons in the conduction band are characterized by migrating into the substance, which is then absorbed onto the surface of the photo-catalystic semiconductor, enabling the reduction of the absorbate. Positive hole in the valence band are characterized by drawing the electrons out of a substance which has been absorbed onto the surface of the photo-catalystic semiconductor, enabling the oxidization of the absorbate.
In titanium oxide (TiO2) that has the photo-catalystic function, electrons that have transited to the conduction band reduce oxygen in the atmosphere and generate a superoxide anion (·O2−), along with which, positive hole that have been generated in the valence band oxidize absorption water on the surface of the titanium oxide, and generate a hydroxyl radical (·OH). The hydroxyl radical has very strong oxidizability. Consequently, when an organic substance is absorbed into photo-catalystic titanium oxide, the organic substance may be broken down into water and carbon dioxide due to the effect of the hydroxyl radical.
Titanium oxide that can accelerate the oxidative breakdown reaction in an organic substance based upon the photo-catalystic function is widely used in anti-bacterial agents, disinfecting agents, anti-fouling agents, deodorants and environmental agents generally. However, the titanium oxide itself lacks the function of absorbing some substances on the surface. Therefore, in order to sufficiently benefit from the oxidative breakdown effect of the titanium oxide based upon its photo-catalystic function and the anti-bacterial effect and the anti-fouling effect by extension, it is necessary to improve the contact efficiency between a subject broken down by oxidization, and the titanium oxide.
Technologies that aim at the improvement of the contact efficiency between the breakdown subject and titanium oxide, for example, are disclosed in JP-A-2001-191458 and 2002-126451. In these technologies, an inclusion of powdered titanium oxide and powdered pre-determined hydroxyapatite (HAP) is used. HAP, in general, has a high absorption power. In the technologies in the above-mentioned publications, situating HAP with a high absorption power in the vicinity of the titanium oxide results in the improvement of the contact efficiency between a breakdown subject and the titanium oxide.
However, according to JP-A-2001-191458 and 2002-126451, since titanium oxide and HAP disperse within a pre-determined binder as mutually independent particles, titanium oxide particles where its contact efficiency with a breakdown subject will not be sufficiently improved may exist. In the case that separation between the titanium oxide particles and the HAP particles are comparatively great, the contact efficiency of the breakdown subject to the titanium oxide particles will not be sufficiently improved.
Another technology that aims at the improvement of the contact efficiency between a breakdown subject and titanium oxide, for example, is disclosed in JP-A-2000-327315. In the publication, a photo-catalystic apatite where a substance, for example, titanium oxide, that has a photo-catalystic function, and another substance, for example, calcium hydroxyapatite (CaHAP), that excels in its capacity to absorb particularly an organic substance, such as protein, are conjugated at the atomic level, is disclosed. The photocatalysitic apatite specifically has a crystal structure where Ti has been substituted for a portion of Ca comprising CaHAP (Ca10(PO4)6 (OH)2), and a titanium oxide-like substructure, which approximates the chemical structure of the photo-catalystic titanium oxide, formed at a site where the Ti has been introduced. Since the titanium oxide-like substructure where the photo-catalystic function can be demonstrated is inherent in the crystal structure of CaHAP, which excels in the absorptivity of an organic substance, the contact efficiency between an organic substance—a breakdown subject—and the titanium oxide-like substructure is effectively improved. As a result, it becomes possible to effectively break down an organic substance by oxidizing such things as finger grease or bacteria cell membranes in a titanium oxide-like substructure.
Kneading or adhering the photo-catalystic apatite to a pre-determined member in an electronic device enables the provision of excellent anti-bacterial and anti-fouling properties to the member. From the viewpoint of improving anti-bacterial and anti-fouling properties, the more the photo-catalystic apatite is kneaded or adhered to the member, the better. However, according to a manufacturing method for the photo-catalystic apatite disclosed in the above-mentioned Publication of Japanese Laid-Open Patent application 2000-327315, the photo-catalystic apatite is obtained as a white powder. Consequently, if the photo-catalystic apatite is used as an anti-bacterial agent or an anti-fouling agent, an essential color tone of the member may be affected because the photo-catalystic apatite is white. Further, the photo-catalystic apatite has a tendency for fine particles to agglomerate with each other in a solvent, which tendency may affect the texture of the member due to the agglomeration. In electronic devices, such as laptop computers or cellar phones, there are many cases where this nonconformity should be avoided relative to a chassis, or a transparent cover for display screen protection.
If the quantity for use of the photo-catalystic apatite is simply reduced for the purpose of avoiding the appearance of non-conformity, it tends to proportionally reduce the anti-bacterial effect and the anti-fouling effect of the photo-catalystic apatite on the surface of the member. Consequently, when using the photo-catalystic apatite as an anti-bacterial agent or an anti-fouling agent, it is difficult to avoid the appearance of nonconformity while the anti-bacterial effect and the anti-fouling effect are highly maintained. Therefore, in electronic devices, such as laptop computers or cellar phones, it has not been conventionally practical to use a photo-catalystic apatite as an anti-bacterial agent or an anti-fouling agent.
In the meantime, stains that adhere on the electronic devices, such as laptop computers, may be removed by a wiping operation. Even in the case where anti-fouling properties are added to a pre-determined member in the electronic device by kneading or adhering the above-mentioned photo-catalystic apatite, since the catalystic function of the photo-catalystic apatite decreases especially under conditions where the quantity of light irradiation is small, the necessity of the operation to wipe the stains is high. However, if the wiping operation is excessively performed, it tends to remove the photo-catalystic apatite particles from the member surface, so the anti-bacterial effect and the anti-fouling effect based upon the photo-catalystic oxidative breakdown effect of the photo-catalystic apatite on the member surface may deteriorate.